1. Field of the Invention
The present invention relates to a computer, such as a personal computer, which has resume function of hibernation type.
2. Description of the Related Art
Battery-driven, portable personal computers have resume function. When a personal computer of this type is switched off, or more precisely when its power switch is turned off, the data items representing the conditions the display panel, the computer and the application program assume immediately before the power switch is turned off are saved in a memory which is driven by the battery. When the power switch is turned on, the display panel, the computer and the application program resumes the conditions represented by the data items saved in the battery-driven memory. Thus, the personal computer can be operated again in exactly the same conditions it assumed when the power switch was turned off. Saving these data items in the memory when the computer is turned off is known as "suspend operation." Thanks to the resume function, the information and the status data respectively stored in the main memory and the CPU internal resister can be saved when the power switch is turned off and can be restored when the power switch is turned on.
The backup power supply for the memory required to achieve the resume function is a rechargeable battery one or an auxiliary dry cell. If the power remaining in the chargeable battery or auxiliary dry cell is not enough to complete the resume function, the data items to be saved in the memory will be erased when the resume function is performed.
To prevent such erasure of data items, new type of resume function called "hibernation" has been developed. Hibernation-type resume function saves the data items the computer requires to resume its operating conditions, on the hard disk incorporated in the hard disk drive (HDD) of the personal computer. The hibernation-type resume function can be performed with no backup power supply for a memory. Hence, the power supply to the computer is completely stopped when the power switch is turned off.
Portable computers recently developed and known as "notebook type" incorporate a small, large-capacity HDD. A notebook-type portable computer is provided with hibernation-type resume function, so that the data items representing the operating conditions of the computer and application program may be saved on the hard disk incorporated in the HDD. The HDD requires no backup power supply, because it is a nonvolatile memory. The HDD stores data almost eternally after the power supply to the computer is completely stopped.
Therefore, it can serve to accomplish a reliable resume function.
A computer having hibernation-type resume function has some problems, as will be explained below.
First, for the following reason, the computer may fail to resume the last operating conditions when it is switched on again. A great amount of data is stored exclusively in the HDD, unlike in a computer having normal-type resume function achieved by the use of a memory and a backup battery. In some cases, the HDD which is designed as an external memory device for storing a large amount of data may have no empty storage areas or insufficient empty storage areas when it is necessary to perform the resume function. Assume that the computer is turned off in this condition, whereby the resume function is performed. Then, the data items representing the operating conditions of the computer cannot be saved in the HDD, disabling the computer to resume the operating conditions when it is turned on again.
Since the HDD is controlled on the basis of the file-control scheme of the operating system (OS) installed in the computer (e.g., the FAT control of MS-DOS), the storage area of the HDD, provided for the resume function, is controlled as a resume-function file. Hence, the resume function cannot work if set by any other operating system.
Second, since the access speed of the HDD is lower than that of an IC memory or the like, some time is required to write the data items stored in the main memory, onto the hard disk when the computer is turned off, and to read the data items from the hard disk when the computer is turned on. A considerably long time inevitably lapses until the data items saved on the hard disk is written back into the main memory, particularly when the power switch is turned on immediately after it is turned off to write the contents of the main memory onto the hard disk by virtue of the resume (suspend) operation. Hence, if the hibernation-type resume function is applied to a portable personal computer (e.g., a notebook-type computer), it will impair the operability of the portable personal computer.
Third, the data items stored in the HDD by the resume operation will be erased if the HDD is detachable one and removed from the personal computer to be replaced with an HDD having a larger storage capacity. If the HDD is set in the computer of another user, the data items saved in the HDD can be accessed by the other user. Here arises a so-called security problem.
Fourth, hibernation-type resume operation consumes far more power than normal-type resume operation. This is because much power is required to drive the HDD in the hibernation-type resume operation, whereas a small amount of power is sufficient to save the data items in a battery-driven memory in the normal-type resume operation. The battery loaded in a portable personal computer has but a small capacity. The amount of power it accumulates by a single recharging is much limited. The power remaining in the battery may not be sufficient to drive the HDD when the computer is turned off. In this case, the data items which the computer needs to resume its last operating conditions cannot be saved in the HDD. In other words, the hibernation-type resume function cannot work at all.
Fifth, the data items cannot be saved on the hard disk, making it possible to carry out the hibernation-type resume operation, when the discontinuous empty storage areas found on the hard disk fail to provide a storage area large enough to store the data items. Even if the discontinuous empty storage areas constitute a sufficient storage area, it takes much time to access all these empty storage areas, inevitably lengthening the time for performing the hibernation-type resume function. In this regards, it should be noted that the storage areas on the hard disk, allocated to the hibernation-type resume function, are controlled by, for example, FAT (File Allocation Table) scheme.